Facile synthesis of submillimeter sized graphene oxide by a novel method

High-quality graphene oxide (GO) was synthesized in two steps. First, graphite on the anode was expanded in an aqueous sulfuric acid solution at a constant direct-current power supply, then it is used to synthesize GO by an improved Hummers method. The synthesized GO had a low layer number (less than five layers) and large lateral size (at least 300 μm).